Will the gas in my Prius Prime go bad if I almost never use it?

Short answer: Yes, gas can go stale, but the Prius Prime is built for this. Owners say the manual covers it and the car can run the engine to use up old fuel. If you go months on battery, buy only a few gallons at a time, add a fuel stabilizer, and let the engine run once in a while.

Symptom: You drive mostly on electric power, the gas gauge barely moves for months, and you're worried the fuel will go bad.

What to check first

1. Read the owner's manual section on fuel and the engine-maintenance mode.
2. Note when you last filled up.
3. Add a fuel stabilizer if the tank will sit for months.
4. Fill with only a few gallons at a time so fresher fuel goes in more often.

Likely causes

1. Fuel sitting for months unused. Gasoline slowly breaks down. If you only drive on electricity, the same tank can sit for many months.
2. Car prompting to burn old fuel. Owners report the manual and the car warn about old fuel and can run the engine to use it up.

What it usually costs

Owners in these threads didn't post prices.

Is it safe to keep driving?

Yes. Old fuel isn't a safety problem by itself, but if the engine runs rough or the check-engine light comes on, have it checked.

DIY or shop?

Stabilizer and small fill-ups are DIY. Rough running is a shop check.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists recall 21V734000 for some 2022 Prius Prime: engine computer software may falsely detect an error and shut down the hybrid system, causing a loss of drive power. It isn't about stale fuel, but it's worth checking on a 2022. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 51 keyword-matched complaints for Toyota Prius Prime 2017–2022 (of 201 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-30; keywords: fuel, gas, stale, engine) (NHTSA returned no data for 3 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 2019 Toyota Prius Prime - Stale Gas a Problem? on Car Talk, a 2019 Prius Prime owner who drives almost all-electric asked about stale gas. Members mentioned the car's own fuel-age notice, using a stabilizer like Sta-Bil, and buying small amounts at a time. They also said regular-octane fuel doesn't need to be premium.
• In 2020 Toyota Prius Prime - Unused Fuel on Car Talk, a 2020 Prius Prime owner was hardly using gas. A member pointed to the section around page 104 of the owner's manual that covers how the car handles old fuel.
• In Would gas go bad in my Prius Prime? on Car Talk, a shopper planning to drive mostly on electricity asked if gas really goes bad. Members said fuel can start to degrade in about 6 months and suggested a stabilizer and keeping the tank part-full with fresh fuel.

Quick tip

If you're mostly electric, treat the gas tank like a lawn mower's. A little fresh fuel and stabilizer go a long way.

Vehicle focus: Toyota Prius Prime plug-in hybrid, 2017-2022.

Safety / mechanic note

If the hybrid system shuts down or shows warnings, Verify with a mechanic.